The present invention relates to a new desalinization apparatus for obtaining potable water, irrigation water or industrial use water from saline water such as seawater. More particularly, the invention relates to a desalinization apparatus which reduces energy requirements by using the latent heat of condensation of water vapor in the evaporation of the saline water.
Many desalinization apparatuses have been produced, and a number of them are being used commercially. The key factor in these apparatuses is to produce a maximum amount of potable water with a minimum of energy input. Desalinization is conventionally effected either by making use of a temperature-dependent change in phase such as evaporation or freezing or by the application of pressure such as in reverse osmosis. The former methods involve the release of latent heat, and, in particular, the latent heat of evaporation is as great as 540 cal. per gram of water, and must be recovered to increase the heat utilization efficiency of the desalinization operation. The change in phase occurs at a fixed temperature for a constant pressure, so recovery of the latent heat must always be accompanied by a change in pressure.
Saline water can also be desalinized by multi-stage flashing, wherein the temperature and pressure of the saline water to be evaporated are increased by heating and the pressure is then reduced to atmosphere so as to evaporate the saline water and condense water vapor. Since this method recovers part of the latent heat of evaporation in the water vapor, it has the highest efficiency of heat utilization and is currently in wide use. But this method has one serious defect: to achieve more efficient use of the heat, no gas (such as air) should be present in the saline water to be evaporated and thus degasification is necessary before elevating the temperature and pressure. Multi-stage flashing has this drawback since it is effected in an airtight system under pressure.